1. Field of the Invention
This invention relates to apparatus and a method for sensing deposition of a thin film layer of a material from a source onto a substrate and more particularly applies to an apparatus and method for sensing the mass per unit area, thickness or deposition rate of a thin film formed of one or more layers of material being deposited on a selected surface of a substrate in a vapor deposition process utilizing one or more of a plurality of detecting means in a preselected array.
2. Description of the Prior Art
There are several known techniques in the prior art for measuring the mass per unit area or thickness of a thin film layer of material being applied to a substrate.
It is known in the prior art to utilize a thin film detector having a detecting surface positioned to intercept a portion of the material being emitted from the sources such that the detecting surface and substrate surface have a thin film layer of material deposited thereon under similar conditions. By monitoring the mass per unit area, thickness or deposition rate of the material being applied to the detecting surface, the mass per unit area or thickness of the thin film layer of material being applied to a selected surface of a substrate can be monitored and controlled.
One known method of measurement of evaporated film thickness during evaporation has been accomplished using optical devices for optically sensing the thickness of a thin film on a detecting surface. Further, it is known in the art to change the resonance frequency of a piezoelectric crystal which occurs during formation of a film of material on the surface of the piezoelectric crystal.
Another known prior art method is to measure the resistance of a thin film conductive layer as it is formed on the substrate or a detecting means surface. The resistance of the thin film layer of material varies in magnitude as a function of the thickness of the thin film of material.
It is also known in the art to measure vapor concentration of the material being evaporated. Certain of the prior art systems utilize a mechanical chopper for modulating the beam of evaporating material so that it can be separately measured from the effect of the residual gas within the vacuum chamber in the deposition process.
In addition, a number of known systems are commercially available for measuring the thickness of a film of material applied to a substrate. One such system utilizing a piezoelectric crystal is offered for sale and sold by Sloan Technology of Santa Barbara, Calif. under the name "DTM" Monitoring System. Another such system utilizing the vapor concentration techniques is offered for sale and sold by Leybold-Heraeus, East Syracuse, N.Y. under the name "INFICON Sentinel 200" deposition controller.